The present invention relates to a new and improved construction of a headbox for a papermaking machine.
Generally speaking, the headbox arranqement of the present development is of the type containinq an infeed channel for the stock suspension or pulp which is being processed. Merging with this infeed channel is a nozzle channel which converges in the direction of an outlet gap or slice. The nozzle channel is bounded by two lips or lip members. One of these lip members possesses at its inner surface at least one step portion extending transversely with respect to the primary flow direction of the stock suspension. This step portion is formed by an essentially flat or planar partial surface of the inner surface and an end surface disposed transversely with respect to the primary flow direction. This flat or planar partial surface extends in the lengthwise direction of the headbox in a manner corresponding essentially to the primary flow direction of the stock suspension.
In European Patent Application No. 0 015 670, filed Feb. 14, 1980 and the cognate U.S. Pat. No. 4,345,970 there is disclosed a prior art headbox arrangement of the aforementioned type. Here, the step portions are formed at the underside of an upper lip which is curved in a convex fashion with respect to the stock suspension. This upper lip or lip member extends from the top towards the bottom of the headbox arrangement. This upper lip is prolonged by a rigid lip portion which protrudes past the outlet gap. At the lower lip or lip member there is attached at the outlet gap a flexible, foil-like lip portion which bears by means of its free end upon a movable web of a sheet forming device. The rigid lip portion of the state-of-the-art equipment serves for guiding the flow of the stock suspension effluxing out of the nozzle channel.